1. Field of the Invention
The invention relates generally to driving force transmission device control apparatuses and control methods. More particularly, the invention relates to an apparatus and a method for controlling a driving force transmission device to transmit a driving force between a pair of rotary members by a friction clutch.
2. Description of the Related Art
Japanese Patent Application Publication No. 2015-116891 (JP 2015-116891 A), for example, discloses a driving force transmission device to transmit a driving force between a pair of rotary members by a friction clutch. Such a driving force transmission device is conventionally used to transmit a driving force for a vehicle, for example.
The driving force transmission device disclosed in JP 2015-116891 A includes: an electric motor; a decelerating mechanism to decelerate the rotation of the electric motor; a cam mechanism to be actuated by the decelerated rotational force of the electric motor; and a friction clutch to be pressed by an axial cam thrust produced by the actuation of the cam mechanism. The driving force transmission device transmits a driving force between rotary members using the frictional force of the friction clutch. The friction clutch is a multiplate wet clutch including a plurality of axially aligned clutch plates lubricated with lubricating oil so that sliding of the clutch plates is facilitated. The clutch plates receive the cam thrust from the cam mechanism so as to come into frictional engagement with each other.
The driving force transmission device is preferably configured to increase gaps between the clutch plates in order to reduce drag torque when the cam mechanism is not being actuated. Increasing the gaps between the clutch plates, however, increases the length of time required between the start of rotation of the electric motor and driving force transmission effected by the frictional engagement of the clutch plates of the friction clutch. In other words, the driving force transmission device will have reduced responsiveness.
To increase the responsiveness, a gain used for feedback control of the electric motor may be set at a high level. In such a case, however, self-excitation vibration and/or overshoot are/is likely to occur. Self-excitation vibration is a phenomenon where a driving force transmitted through the friction clutch changes in short cycles. Overshoot is a phenomenon where a driving force larger than a desired driving force is temporarily transmitted. Occurrence of self-excitation vibration and/or overshoot reduces the accuracy of the driving force to be transmitted.